Despite uncertainties in our understanding of early Earth volcanism and atmospheric composition, thermodynamic modelling is able to offer estimates of the global production of reactive trace species (NO, OH, SO3, Cl, Br and I) from early Earth volcanism, and thereby to shed light on processes which may have been different in Earth’s early atmosphere. Model results show that thermal decomposition of magmatic H2O, CO2 and SO2 in high-T mixtures of magmatic and atmospheric gases (at T > 1400 °C) generate high levels of reactive trace gas species. Production of these reactive trace species is insensitive to atmospheric CO2 in mixtures where the atmospheric gas is the minor component and will hence continue during periods of low atmospheric CO2. Fluxes of NO, OH, Cl, Br and I from early Earth volcanism are predicted to exceed those from modern Earth volcanism as the higher temperature of early Earth emissions compensates for lower levels of O2 in the atmosphere, compared to the modern Earth. Under certain conditions, the volcanic NO flux from early Earth volcanism is found to be comparable to other sources of reactive N such as lightning NO and photochemical HCN. This is one possible source of fixed nitrogen which may alleviate any postulated Archean nitrogen crisis. Our thermodynamic model reveals that production of SO3 (a potential precursor for near-source volcanic sulphate and hence ‘primary’ volcanic aerosol) is likely to be significantly lower from early Earth volcanism. Uncertainty in the pathway to near-source sulphate in modern volcanism (i.e., the reaction of SO3 with water or direct emission) introduces a large uncertainty into the production rate of near-source volcanic sulphate on the early Earth. 相似文献
Mass concentrations of PM10, PM2.5, and black smoke (BS) were measured in April 2003 during a 3-week campaign in a small village and at a nearby background location in the central part of the Czech Republic. In a pilot analysis, concentrations of selected trace elements (Al, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Sr, Cd, Sb, Cs, Pb) in the collected aerosol were determined by means of ICP-MS. Average concentrations of both PM fractions and BS were higher in the village (37, 26 and 26 μg m−3) than at the background location (26, 19 and 11 μg m−3) for PM10, PM2.5 and BS, respectively. Both PM10 and PM2.5 were reasonably correlated in the village (r = 0.80) and also at the background location (r = 0.79). Correlation between same fractions from the village and from the background site were even higher (r = 0.97 and r = 0.95 for the PM10 and PM2.5, respectively) suggesting that most of the aerosol in both locations may be influenced by similar sources. The ratio between PM10 and PM2.5 showed that sources in the village contributed about 33% and 35% to local aerosol concentration for PM10 and PM2.5, respectively. When the data from the two rural locations were compared with corresponding 24-h averages of PM10 concentrations obtained for the period of the campaign from fixed site monitors situated near larger towns, the highest concentration was found in Prague the Czech capital (49 μg m−3) followed by a district town Beroun (41 μg m−3) and the village (37 μg m−3). The lowest PM10 concentration was found in the village background (26 μg m−3). Elemental analysis revealed higher concentrations for most of the elements characteristic of combustion aerosol (namely Zn, Pb, As, Mn and Ti) in the PM collected in the village. The results support the idea that traditional heating in villages may contribute a great extent to local air pollution and may represent an important problem. 相似文献
Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that
the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage
on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day
and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal
shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods
were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly
shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs.
Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm,
tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude
that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which
are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing
bare sand on theiry way to a feeding habitat rich in valuable prey. 相似文献
U-Th rich mineral inclusions in apatite are often held responsible for erroneously old (U-Th)/He ages, because they produce “parentless” He. Three aspects associated with this problem are discussed here. First, simple dimensional considerations indicate that for small mineral inclusions, the parentless helium problem might not be as serious as generally thought. For example, a mineral inclusion that is 10% the length, width and height of its host apatite needs to be a thousand times more concentrated in U and Th to produce an equal amount of He. Therefore, single isolated inclusions smaller than a few μm are unlikely to contribute significant helium. For larger or more abundant inclusions, the parentless helium problem can be solved by dissolution of the apatite and its inclusions in hot HF. Second, besides creating parentless helium, inclusions also complicate α-ejection corrections. Mathematical exploration of this latter problem for spherical geometries reveals that for randomly distributed inclusions, the probability distribution of single-grain ages is predicted to have a sharp mode at the mean age, with tails towards younger and older ages. Multiple-grain measurements will yield accurate and precise age estimates if 10 or more randomly distributed α-emitting mineral inclusions are present in a sample. Third, thermal modeling indicates that mineral inclusions have a non-trivial but minor (<5 °C) effect on the closure temperature. These predictions were tested on apatites from rapidly cooled migmatites of Naxos (Greece) which contain abundant U-rich zircon inclusions. Thirty-seven samples were subjected to two kinds of treatment. The “pooled” age (i.e., the synthetic multi-grain age computed from a number of single-grain analyses) of four inclusion-free samples (13 apatites), prepared in HNO3 is 10.9 Ma, close to apatite and zircon fission-track ages from the same rock. (U-Th)/He ages of 14 inclusion-bearing samples dissolved in HNO3 range between 9 and 45 Ma, with a pooled age of 22.6 Ma. The ages of 19 HF-treated samples range between 5 and 16 Ma, with 10 of 14 single-grain samples between 9 and 13 Ma and a pooled age of 10.9 Ma. These observations agree with the theoretical predictions and support the addition of HF-treated apatite (U-Th)/He dating to the thermochronological toolbox. 相似文献
Changes in size distribution and elemental composition of 0.5-50 nm fresh water colloids during estuarine mixing have been studied by in-laboratory mixing of natural creek water and synthetic seawater, followed by size fractionation with Asymmetrical Flow Field-Flow Fractionation, and online elemental quantification by High-Resolution ICPMS. At least two types of colloids were present in the studied size region; 0.5-3 nm fluorescent dissolved organic matter (FDOM), and >3 nm colloids that were rich in Fe and colored dissolved organic matter (CDOM). Most trace elements were associated in different proportions to these two populations of colloids. Following mixing with synthetic seawater, the >3 nm Fe-rich colloids and CDOM were extensively removed from the studied size region by salt induced aggregation. The degree of removal with increasing salinity was greatest below 2.5‰ salinity, continued to a lesser degree between 2.5‰ and 15‰ salinity, above which only very small additional removal could be distinguished. At 25‰ salinity, the Fe concentration in the 0.5-50 size region had been reduced down to 15% of its original value in freshwater, while the amount of CDOM had been reduced to 55%. On the contrary, the concentration of the 0.5-3 nm FDOM was unchanged by the increased concentration of sea salt. Therefore, colloidally associated Al, P, Co, Cu, Zn, Ce, Lu and Pb were removed from the 0.5-50 nm size region according to their relative distributions between the FDOM and the Fe-rich colloids. Consequently, at 25‰ salinity, the 0.5-50 nm concentrations of Al, Mn, P and Pb, (mainly associated with the Fe-rich colloids) had been reduced down to 13-26 % of their values in freshwater, while the concentrations of Co and Cu (with higher preferences for FDOM) were less reduced, down to 46% and 57%, respectively. Changes in the elemental composition of the remaining colloidal matter were observed, the most pronounced were increased contents of P, Al and Pb in Fe-rich colloidal matter of medium size (∼3-15 nm) and increased Pb content in Fe-rich colloidal matter of larger size (∼5-50 nm). 相似文献
Natural Hazards - The deltaic coast of Myanmar was severely hit by tropical cyclone Nargis in May 2008. In the present study, a top-down numerical simulation approach using the Weather Research and... 相似文献
Karst researchers of the Karst Research Institute ZRC SAZU are regularly consulted during the planning of Slovenia’s motorways
and invited to observe and monitor construction in the karst areas. More than 350 caves have been discovered in the course
of building 60 km of new motorways over the past decade. Access to the most important caves is preserved by concrete tubes
closed with metal covers at the roadside. The largest cave system in a tunnel, named LC-S647, is almost entirely preserved.
The protection of this cave will serve as a good example for the preservation of natural heritage in the future. Construction
work for the motorway uncovered a high degree of karstification. In particular, the discovery of this cave in the Kastelec
tunnel LC-S647 showed the existence of a major cave system in the geological and speleological past. A number of unconnected
passages have also been found. Caves discovered during highway construction have brought new knowledge about the cavernosity
and the geological history of this part of the karst. 相似文献
Karst aquifers represent important water resources in many parts of the world. Unfortunately, karst aquifers are characterised
by high contamination risks. This paper presents a travel time based method for the estimation of karst groundwater vulnerability.
It considers (1) physics-based lateral flow within the uppermost weathered zone (epikarst) in a limestone-dominated region
and (2) high velocities of vertical infiltration at discrete infiltration points (e.g. sinkholes) or lines (e.g. dry valleys,
faults). Consequently, the Transit Time Method honours the actual flow path within the unsaturated zone of a karst aquifer
system. A test site in Northern Jordan was chosen for the demonstration of the assessment technique, i.e. the catchment area
of the Qunayyah Spring north of the capital Amman. The results demonstrate that zones of highest vulnerability lie within
valleys and nearby main fault zones. It also reveals that regions, categorised as protected areas by other methods due to
thick unsaturated zones, contribute to a major degree to the total risk. 相似文献
Satellite altimetry has been widely used to determine surface elevation changes in polar ice sheets. The original height measurements are irregularly distributed in space and time. Gridded surface elevation changes are commonly derived by repeat altimetry analysis (RAA) and subsequent spatial interpolation of height change estimates. This article assesses how methodological choices related to those two steps affect the accuracy of surface elevation changes, and how well this accuracy is represented by formal uncertainties. In a simulation environment resembling CryoSat-2 measurements acquired over a region in northeast Greenland between December 2010 and January 2014, different local topography modeling approaches and different cell sizes for RAA, and four interpolation approaches are tested. Among the simulated cases, the choice of either favorable or unfavorable RAA affects the accuracy of results by about a factor of 6, and the different accuracy levels are propagated into the results of interpolation. For RAA, correcting local topography by an external digital elevation model (DEM) is best, if a very precise DEM is available, which is not always the case. Yet the best DEM-independent local topography correction (nine-parameter model within a 3,000 m diameter cell) is comparable to the use of a perfect DEM, which exactly represents the ice sheet topography, on the same cell size. Interpolation by heterogeneous measurement-error-filtered kriging is significantly more accurate (on the order of 50% error reduction) than interpolation methods, which do not account for heterogeneous errors.